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Biomedical subjects

A H Linton

Publications and source records attributed to A H Linton.

At least 37 records · Page 2Linked to original sources
PubMed1985

The ecology of Escherichia coli in market calves fed a milk-substitute diet.

Dynamic changes in the Escherichia coli population in the calf gut were studied over 21 days in a group of 18 intensively-reared market calves. Isolates were identified by O-serogrouping, biotyping and resistogram patterns. Seventy O-serogroups were identified among nearly 3000 E. coli isolates examined and these were subdivided into 416 strains by means of their biotype and resistogram. Seventy-five per cent of these strains were detected only once or twice, which points to the continual replacement of the E. coli flora with strains that showed low persistence in the gut. The rise in the frequency of antibiotic resistance observed during the study was not due to a change in the proportion of resistant to sensitive strains in the gut flora. It was a consequence of the displacement of the original flora by multiply-resistant strains, which presumably originated from the calves' environment.

Animal Feed↗
PubMed1985

The ecology of Escherichia coli in calves reared as dairy-cow replacements.

A continual turn-over in the strains forming the majority of faecal Escherichia coli flora was demonstrated in 16 calves reared as dairy cow replacements. The incidence of antibiotic resistance among isolates, as measured by an Antibiotic Resistance Index (ARI), changed markedly with the age of the calf. The value was low initially, when the calves were 1-2 days old and housed with adult animals. It then rose rapidly during the first week after the animals had been weaned and moved into nursery pens. This change in ARI was associated with the isolation of strains resistant to four or five of the six drugs included in the sensitivity test. The ARI then fell from the third week to low levels by the time that the calves were five months of age. This fall was due to the isolation of an increasing proportion of sensitive E. coli strains. These differed from the sensitive strains which had colonized the calves in the early days of life so demonstrating that the change was not due to the reemergence of strains identified several weeks previously. The source of E. coli strains was presumed to be the calfs' environment but further investigations are required to prove this conclusively.

Animals↗
PubMed1985

A comparison of the ecology of Escherichia coli in the intestine of healthy unweaned pigs and pigs after weaning.

A total of 51 clinically healthy pigs (14 unweaned and 37 weaned) from five litters, and aged 21 to 35 d, were studied. Escherichia coli isolates from the duodenum, jejunum, ileum, caecum and colon were differentiated on the basis of O-serogroup, biotype and resistance pattern. The complexity of the flora was influenced considerably by the presence or absence of the enterotoxigenic serotype 0149: K91, K88a,c (Abbotstown strain). When it was absent the E. coli flora of both weaned and unweaned pigs was complex with up to 25 strains being identified. The majority of these E. coli strains identified in each pig were isolated from only one of the five intestinal sites sampled. On the other hand, when the enterotoxigenic strain was present (14 pigs) it tended to dominate the E. coli flora at all levels of the intestine and this dominance was reflected in a corresponding fall in the total number of E. coli strains isolated per pig.

Animals↗
PubMed1985

Monitoring for antibiotic resistance in enterococci consequent upon feeding growth promoters active against gram-positive bacteria.

Commercial chicken and pig farms, using different growth promoters, were monitored for enterococci resistant to a range of antibacterial agents. Due to inconsistent findings attributed to uncontrollable factors, chickens kept under experimental conditions were also studied. A total of 4216 isolates from all the surveys were examined. Resistant isolates were often encountered, even in control groups, suggesting complex population changes not necessarily solely connected with the influence of the growth promoters. It was concluded that comprehensive methods for differentiating strains are necessary to unravel this problem.

Animals↗
PubMed1985

The influence of flumequine on the resistance of the coliform flora of chickens to the agent.

Flumequine (1 g/l) was administered to healthy young chickens in the drinking water for 5 days. A transient increase in the incidence of resistance to flumequine (4 micrograms/ml) was recorded in faecal coliform isolates after administration. Cross-resistance with nalidixic acid was demonstrated, but there was no evidence of cross-resistance to ampicillin, chloramphenicol, kanamycin, streptomycin, sulphadiazide, tetracycline and trimethoprim.

Animals↗
PubMed1984

Further observations on the excretion of salmonella in the faeces of calves fed milk substitute.

Swabs of rectal faeces were obtained daily for 28 days from 90 calves reared in five batches during the summer of 1983. The calves were purchased unweaned in markets and fed a milk-substitute diet. Salmonella typhimurium phage type DT204c was isolated from calves in four batches and Salmonella newport from one. When the data from the 90 calves were considered together the incidence of salmonellas, excretion rose to peak between 5 and 7 days after purchase before declining to low levels during the fourth week. Salmonella was isolated from 55 (61%) calves; 30 were positive on up to four occasions while 21 and 4 animals respectively were positive between 5 and 11 and 15 and 20 times. In the majority of animals infection was probably subclinical since treatment with antibacterial drugs and excretion of S. typhimurium coincided in four calves only.

Animal Feed↗
PubMed1984

The persistence of drug resistant Escherichia coli strains in the majority faecal flora of calves.

Two groups of calves, one of three and the other of two animals, were purchased in markets and reared initially on a commercial veal unit for 1 month and 4 months respectively. They were then moved to the Veterinary School, Langford, and kept for a further 6 and 4 months respectively. The animals were sampled weekly and a continual turnover in the strains forming the majority Escherichia coli faecal flora was demonstrated for all calves. Antibacterial-drug resistance, as measured by an Antibiotic Resistance Index (ARI), increased after arrival on the veal unit and persisted at high levels during the whole of their stay. After moving to Langford the ARI fell. Initially there was a reduction in the average number of resistance determinants per resistant strain and then, after a delay of up to 8 weeks, by an increase in the proportion of isolates that were fully sensitive. The source of the sensitive strains was not ascertained, although their appearance was not associated specifically with either weaning or turning out to pasture.

Animals↗
PubMed1983

The excretion of Salmonella typhimurium in the faeces of calves fed milk substitute.

A total of 495 calves in 16 batches were examined (117 calves in 4 batches in 1979 and 378 in 12 batches in 1982). They were purchased in markets, transported by road to a farm in Somerset and reared on a milk substitute diet for a period of up to five weeks. Salmonella typhimurium phage type DT 193 was endemic in 1979 and phage type DT 204c in 1982. The mortality rates in the two years were 9.4% and 1.9% respectively. The causes of death were not investigated although the majority were probably due to salmonellosis. The rate of isolation of S. typhimurium from the rectal faeces of calves in all groups was either zero or relatively low on arrival. It rose to a peak (which was higher in 1979) in the second or third weeks before declining to low levels by the end of the fourth week of residence on the farm. Data from 162 calves, examined twice weekly for four weeks in 1982, indicated that the distribution of infected calves, based on the number of times that S. typhimurium was isolated from each, was not random. The calves could be assigned to two main categories; those from which the organism was never isolated and those from which it was isolated at least twice. This suggested that salmonella infected calves actively excreted the organism. The association between salmonella excretion and medication of sick animals with antibacterial drugs was strongest during the second week. Over the four-week period nearly 40% of the calves found to be excreting S. typhimurium were not treated, indicating a high incidence of subclinical infection. Salmonella excretion by the calves followed a regular pattern and infection was self-limiting within five weeks. The peak in the salmonella excretion rate and the mortality rate were higher in 1979 when phage type DT 193 was the endemic strain. However, in 1982 the calves received 100 p.p.m. furazolidone in their milk ration during the first week of their stay on the farm, and this may have contributed to the differences noted between the two years.

Animal Feed↗
PubMed1982

The biotyping of Escherichia coli isolated from healthy farm animals.

A total of 2973 Escherichia coli, isolated from six different groups of animals, were examined for their ability to ferment adonitol, dulcitol, raffinose, rhamnose and sorbose in solid media. Twenty-nine fermentation patterns were recorded although 2443 (82%) of the E. coli belonged to seven of the 32 possible biotypes. Ninety-six O-serotypes were identified within the 2973 E. coli. The number of O-serotypes represented in the 15 most common biotypes ranged from three to 15. Serotypes O8 and O9 were found most commonly in the different groups of animals and several biotypes amongst these two O-serotypes were identified in two or more groups of the animals. The ability of the E. coli to metabolize aesculin, ornithine, salicin and sucrose was also assessed. These test proved less reproducible and were not included in the primary biotyping scheme although their use allowed the enumeration of additional biotypes. The application of biotyping to the study of the ecology of drug-resistant strains of E. coli in five situations is briefly presented.

Amino Acids↗
PubMed1982

The survival of multi-antibacterial drug-resistant Escherichia coli and Salmonella typhimurium in stored static slurry from a veal calf unit.

Salmonella typhimurium phage type DT 193 survived in small numbers, in stored static slurry derived from veal calves, for the 7-week period of observation. The viable coliform count fell by 1 1/2 logs during the first 2 weeks of storage, thereafter there were only relatively small fluctuations in the coliform population. In all 735 of 752 Escherichia coli isolates examined from eight samples of slurry were resistant to 3-6 antibacterial drugs. There was no dramatic change in the overall level of drug resistance amongst the E. coli with time. Chloramphenicol resistance was recorded in 400 (55%) of the E. coli. It was always associated with multiple resistance, with 96% of the strains being resistant to 5 or 6 drugs, although the proportion of isolates of each of the ten most prevalent O-serotypes resistant to chloramphenicol was variable and ranged between none and 97.5%. The use of biotyping together with O-serotyping indicated that the E. coli population was extremely complex, although certain components of the population remained relatively stable within the dominant flora with time since several of the more common O-serotype/biotype combinations were isolated from more than half of the eight slurry samples examined.

Animals↗
PubMed1982

The persistence of drug resistant Escherichia coli in the intestinal flora of healthy broiler chicks.

Antibacterial drugs (oxytetracycline, streptomycin and sulphonamides) were included in the drinking water of healthy broiler chicks from the sixth to the twentieth day of life to select a resistant gut flora. On the twenty-first day the birds were divided into three groups and reared in separate rooms until 100 days of age. One group was housed in cages with wire floors while the others were reared on litter. Faeces from adult hens were added regularly to the litter of one of these groups to determine its effect on the gut flora of the chicks. The ecology of Escherichia coli was studied using O-serotyping, biotyping and antibacterial drug resistogram typing. The proportion of E. coli in the dominant faecal flora resistant to two to four antibacterial drugs increased with time to reach a peak several days after the drugs were withdrawn. Thereafter, the level of drug resistance in the E. coli declined equally in all three groups. The majority of organisms with multiple resistance were derived from biotypes of O-serotypes initially resistant to only one drug and were identified before the drugs were administered. The decline in the level of resistance in the dominant faecal flora after the fourth week was due to the appearance of either new O-serotypes or new biotypes of O-serotypes previously shown to be multiply resistant, and which were either sensitive or resistant to only one drug. It is probably that these new strains were derived from the food since several O-serotypes appeared simultaneously in all three groups of birds.

Animals↗